The memo requested U.S. intervention to prevent a military coup and protect the civilian government in exchange for granting the U.S. heavy influence on matters of national security in Pakistan.

Dubbed “Memogate,” the affair has dominated headlines in Pakistan for weeks before apparently claiming its first victim on Tuesday.

A statement issued by Pakistan's Prime Minister Yousaf Raza Gilani's office said Haqqani has been asked "to submit his resignation so that the investigation can be carried out properly."

Haqqani flew back to Islamabad this weekend to explain his involvement – if any -- in the scandal to President Asif Ali Zardari, Prime Minister Gilani and military and intelligence officials, tweeting on Nov. 19th that he was "Heading back to the motherland." He reportedly offered his resignation then, but it was not accepted at the time.

"Memogate" is centered on a memo that Pakistani-American businessman Mansoor Ijaz says he delivered to then-chairman of the U.S. Joint Chiefs of Staff, Adm. Mike Mullen, at the behest of Ambassador Haqqani in the days immediately following the U.S. raid that killed bin Laden in Pakistan. The memo, which is unsigned, states that there had been “a significant deterioration in Pakistan’s political atmosphere” and indicated that the civilian government feared that factions within the military were planning a coup.

Retired U.S. Gen. Jim Jones, President Barack Obama’s former national security adviser, has confirmed that the memo was delivered to Mullen.

The existence of the memo was revealed in an October op-ed by Ijaz for the Financial Times. Ijaz told NBC News he typed the memo as dictated by Haqqani, and only revealed its existence in the article to lend credibility to the policy case he was making. Haqqani has denied any involvement in requesting or drafting the memo. But opposition leaders in Pakistan pounced, equating the memo to "treason" and demanding that heads roll.

Members of the Pakistani press have been digging into the scandal for the last few weeks, including publishing Blackberry messages allegedly exchanged by Haqqani and Ijaz as the memo was being drafted, and afterward.

U.S. officials tell NBC News they are watching with "great interest" how this is being handled by the Pakistani government, but say they are not involved in the investigation.

Haqqani, who has been described as a "seasoned political operator," is well-liked within U.S. government circles, and enjoys a strong reputation for managing to remain effective in a treacherous political climate. He remains in Islamabad at this writing.

In Tuesday’s statement, Gilani ordered an investigation to be "carried out fairly, objectively and without bias."

“As a result of controversy generated by the alleged memo, which had been drafted, formulated and further admitted to have been received by Authority in USA, it has become necessary in the national interest to formally arrive at the actual and true facts,” the statement said.

Haqqani turned back to his Twitter account following the announcement of his resignation, writing, "I have much to contribute to building a new Pakistan free of bigotry & intolerance. Will focus energies on that."